Murphy, C. J.,
delivered the opinion of the Court. Davidson, J., dissents and filed a dissenting opinion at page 365 infra.
We granted certiorari in this case to consider the claim of Hugh J. Courtney that he was erroneously denied “accidental” disability retirement benefits for mental incapacitation suffered as a result of unusual pressures, strains and conditions of his employment as a librarian with the Prince George’s County library system.
Courtney, a member of the Maryland Teachers Retirement System, sought the retirement allowance under the provisions of Maryland Code (1978 Repl. Vol.), Art. 73B, § 86 (4a),1 which authorize the payment of an “accidental disability retirement benefit” to a member who:
“has been totally and permanently incapacitated for duty as the natural and proximate result of an accident occurring while in the actual performance of duty at some definite time and place, without willful negligence on his part ..., provided that the medical board shall certify that such member is mentally or physically incapacitated for the further performance of duty ....”
In filing his claim for accidental disability benefits, Courtney described the “accident” which caused his mental incapacitation in these words:
“A two year period of being severely understaffed, plus a lack of administrative concern for my problems led to severe frustration and depression [358]*358concerning my ability to properly function as an Area Branch Librarian and culminated in my having a nervous breakdown.”
The Medical Board, after considering the evidence submitted to it, including the report of Courtney’s psychiatrist, Dr. Richard Kastner, certified that Courtney was mentally incapacitated for the further performance of duty “due to schizophrenia-paranoid type.” It concluded that he be retired with ordinary disability benefits, rather than accidental disability benefits, because his mental incapacitation was not caused “by the accident reported.”
Courtney appealed to the Board of Trustees of the Maryland Retirement System and a full evidentiary hearing was held on November 7,1977. The evidence before the Board revealed that Courtney began working for the Prince George’s County library system in 1966. He was promoted in 1969 to the position of Area Branch Librarian at Bowie, with responsibility for satellite branches in Laurel and Marlboro. In this capacity, he was faced with numerous problems, including chronic understaffing, repeated and serious incidents of vandalism, inadequate security, and malfunctioning and unsafe equipment. Courtney’s efforts to ameliorate these problems through administrative channels were unsuccessful. As a result, he assumed responsibilities beyond his job description for maintenance and security, worked hours far in excess of his 37% hour contractual work week, and strained his relations with the library administration by constantly calling attention to these problems. Mental, as well as physical stress and strain ensued, as evidenced by a co-worker’s observation that Courtney’s “health deteriorated, he lost a lot of weight, [and] he became more agitated.”
On September 3, 1975, Courtney had a conversation with the area branch librarian from Carrolton concerning understaffing in their respective maintenance departments. Finding the substance of that conversation distressing, Courtney returned to work in Bowie where, after ruminating about work-related problems, “he became severely frustrated [359]*359and depressed.” That afternoon, he suffered a nervous breakdown, evidenced by his pallor, speech incoherency, loud belching, and other peculiar actions. He was hospitalized that evening and remained in the hospital for four days. On September 23, he began psychiatric treatment under Dr. Richard Kastner and has since been unable to work.
The evidence disclosed that Courtney had a history of chronic mental disorder. In July of 1963, while serving in the Navy, Courtney was diagnosed as suffering from paranoid schizophrenia. He was hospitalized for 11 months while receiving treatment for this illness and was subsequently discharged from the Navy with a 100 percent medical disability rating. In 1969, five years after his discharge, his disability was reduced to 30 percent, a disability rating for which he received partial disability payments from the Navy throughout his full-time employment as a librarian.
Dr. Norman Freeman, Jr., a member of the Medical Board, testified that Courtney’s disability was not caused by an accident. He noted Courtney’s earlier extensive hospitalization for the same psychosis in 1964. He said that “the nature of the disease we are talking about is a recurrent disease, a disease which is often in remission and exacerbation, and he had this in 1963. Now we are having a recurrence of it in 1975.”
Dr. Kastner testified on behalf of Courtney. He said that there was no correlation between the 1963 incidence of paranoid schizophrenia and Courtney’s 1975 mental breakdown. He said that the 1963 illness “either had burnt itself out or was extremely quiescent.” He concurred, however, with Dr. Freeman’s earlier testimony “that no doctor knows the cause of schizophrenia or paranoia.” He admitted that Courtney’s mental incapacitation “may have been attributable elsewhere.” Dr. Kastner nevertheless concluded that the psychosis resulted from an “admixture of [Courtney’s] job, the stresses that he had, the mode or method in which he dealt with it, and then the rather unusual interaction between the organization and [Courtney].”
The Board determined from the evidence that Courtney was not entitled to accidental disability retirement benefits. [360]*360It noted that Courtney had been receiving “a partial disability allowance from the Navy for paranoia-schizophrenia since ■1963,” and that the Navy considered Courtney “partially disabled from paranoia-schizophrenia before and during the period in which his present disability arose.” A majority of the five-member Board concluded that the disability was “attributable to a preexisting condition of paranoia-schizophrenia.” Acknowledging that “the conditions under which Mr. Courtney worked contributed to his emotional distress,” the Board nevertheless held that “there is no evidence that he suffered an accidental injury of a character causing the mental condition of which he complains.” A majority of the Board thus determined “that Mr. Courtney’s incapacity for duty is not the natural and proximate result of an accident occurring at some definite time and place while in the actual performance of duty.” Two members of the majority also concurred on the ground that “a mental disability which is not the result of a physical injury is not an accident within the meaning of ... [the statute].” Two members of the Board dissented; they were of the opinion “that the conditions under which claimant worked constituted an unusual condition of employment which caused an accident.”
Courtney filed an appeal to the Circuit Court for Prince George’s County, as authorized by the Administrative Procedure Act, Code (1978 Repl. Yol.), Art. 41, § 255. In affirming the Board, the court stated:
“Notwithstanding Dr. Kastner’s testimony and evidence in the record revealing conditions of employment which might cause great stress and strain (i.e.
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Murphy, C. J.,
delivered the opinion of the Court. Davidson, J., dissents and filed a dissenting opinion at page 365 infra.
We granted certiorari in this case to consider the claim of Hugh J. Courtney that he was erroneously denied “accidental” disability retirement benefits for mental incapacitation suffered as a result of unusual pressures, strains and conditions of his employment as a librarian with the Prince George’s County library system.
Courtney, a member of the Maryland Teachers Retirement System, sought the retirement allowance under the provisions of Maryland Code (1978 Repl. Vol.), Art. 73B, § 86 (4a),1 which authorize the payment of an “accidental disability retirement benefit” to a member who:
“has been totally and permanently incapacitated for duty as the natural and proximate result of an accident occurring while in the actual performance of duty at some definite time and place, without willful negligence on his part ..., provided that the medical board shall certify that such member is mentally or physically incapacitated for the further performance of duty ....”
In filing his claim for accidental disability benefits, Courtney described the “accident” which caused his mental incapacitation in these words:
“A two year period of being severely understaffed, plus a lack of administrative concern for my problems led to severe frustration and depression [358]*358concerning my ability to properly function as an Area Branch Librarian and culminated in my having a nervous breakdown.”
The Medical Board, after considering the evidence submitted to it, including the report of Courtney’s psychiatrist, Dr. Richard Kastner, certified that Courtney was mentally incapacitated for the further performance of duty “due to schizophrenia-paranoid type.” It concluded that he be retired with ordinary disability benefits, rather than accidental disability benefits, because his mental incapacitation was not caused “by the accident reported.”
Courtney appealed to the Board of Trustees of the Maryland Retirement System and a full evidentiary hearing was held on November 7,1977. The evidence before the Board revealed that Courtney began working for the Prince George’s County library system in 1966. He was promoted in 1969 to the position of Area Branch Librarian at Bowie, with responsibility for satellite branches in Laurel and Marlboro. In this capacity, he was faced with numerous problems, including chronic understaffing, repeated and serious incidents of vandalism, inadequate security, and malfunctioning and unsafe equipment. Courtney’s efforts to ameliorate these problems through administrative channels were unsuccessful. As a result, he assumed responsibilities beyond his job description for maintenance and security, worked hours far in excess of his 37% hour contractual work week, and strained his relations with the library administration by constantly calling attention to these problems. Mental, as well as physical stress and strain ensued, as evidenced by a co-worker’s observation that Courtney’s “health deteriorated, he lost a lot of weight, [and] he became more agitated.”
On September 3, 1975, Courtney had a conversation with the area branch librarian from Carrolton concerning understaffing in their respective maintenance departments. Finding the substance of that conversation distressing, Courtney returned to work in Bowie where, after ruminating about work-related problems, “he became severely frustrated [359]*359and depressed.” That afternoon, he suffered a nervous breakdown, evidenced by his pallor, speech incoherency, loud belching, and other peculiar actions. He was hospitalized that evening and remained in the hospital for four days. On September 23, he began psychiatric treatment under Dr. Richard Kastner and has since been unable to work.
The evidence disclosed that Courtney had a history of chronic mental disorder. In July of 1963, while serving in the Navy, Courtney was diagnosed as suffering from paranoid schizophrenia. He was hospitalized for 11 months while receiving treatment for this illness and was subsequently discharged from the Navy with a 100 percent medical disability rating. In 1969, five years after his discharge, his disability was reduced to 30 percent, a disability rating for which he received partial disability payments from the Navy throughout his full-time employment as a librarian.
Dr. Norman Freeman, Jr., a member of the Medical Board, testified that Courtney’s disability was not caused by an accident. He noted Courtney’s earlier extensive hospitalization for the same psychosis in 1964. He said that “the nature of the disease we are talking about is a recurrent disease, a disease which is often in remission and exacerbation, and he had this in 1963. Now we are having a recurrence of it in 1975.”
Dr. Kastner testified on behalf of Courtney. He said that there was no correlation between the 1963 incidence of paranoid schizophrenia and Courtney’s 1975 mental breakdown. He said that the 1963 illness “either had burnt itself out or was extremely quiescent.” He concurred, however, with Dr. Freeman’s earlier testimony “that no doctor knows the cause of schizophrenia or paranoia.” He admitted that Courtney’s mental incapacitation “may have been attributable elsewhere.” Dr. Kastner nevertheless concluded that the psychosis resulted from an “admixture of [Courtney’s] job, the stresses that he had, the mode or method in which he dealt with it, and then the rather unusual interaction between the organization and [Courtney].”
The Board determined from the evidence that Courtney was not entitled to accidental disability retirement benefits. [360]*360It noted that Courtney had been receiving “a partial disability allowance from the Navy for paranoia-schizophrenia since ■1963,” and that the Navy considered Courtney “partially disabled from paranoia-schizophrenia before and during the period in which his present disability arose.” A majority of the five-member Board concluded that the disability was “attributable to a preexisting condition of paranoia-schizophrenia.” Acknowledging that “the conditions under which Mr. Courtney worked contributed to his emotional distress,” the Board nevertheless held that “there is no evidence that he suffered an accidental injury of a character causing the mental condition of which he complains.” A majority of the Board thus determined “that Mr. Courtney’s incapacity for duty is not the natural and proximate result of an accident occurring at some definite time and place while in the actual performance of duty.” Two members of the majority also concurred on the ground that “a mental disability which is not the result of a physical injury is not an accident within the meaning of ... [the statute].” Two members of the Board dissented; they were of the opinion “that the conditions under which claimant worked constituted an unusual condition of employment which caused an accident.”
Courtney filed an appeal to the Circuit Court for Prince George’s County, as authorized by the Administrative Procedure Act, Code (1978 Repl. Yol.), Art. 41, § 255. In affirming the Board, the court stated:
“Notwithstanding Dr. Kastner’s testimony and evidence in the record revealing conditions of employment which might cause great stress and strain (i.e. understaffing, poor security, vandalism, inadequate facilities at the library), the Court after examining all the testimony and documents thereto finds that there was substantial evidence to support the Board’s decision that Mr. Courtney’s present mental incapacity characterized as paranoia-schizophrenia is not a natural and proximate cause of an accident occurring at some definite time and place in the actual performance of duty [as required [361]*361by the statutel, but rather the Petitioner’s mental incapacity was the proximate result of his pre-existing mental illness.”
The court further concluded that its finding that the Board’s decision was based upon substantial evidence made it unnecessary to reach the question of whether an award of benefits for mental disability under the statute must be limited to situations involving physical injury. Nevertheless, after reviewing the relevant Maryland case law, the court found that the two concurring members did not commit an error of law “in ruling that the Petitioner could not receive accidental benefits because his mental disability was not accompanied by physical injury.”
Courtney’s appeal to the Court of Special Appeals was based on his contention that the Board’s finding that his mental incapacitation was attributable to a preexisting psychiatric illness was not supported by the medical testimony in the record and, secondly, that his mental disability was a direct and proximate result of the unusual strain and conditions of his employment at the Bowie library. Additionally, Courtney urged reversal of the view held by the concurring members of the Board which would require accidental disability claimants alleging mental incapacity to show some manifestation of physical injury. Our grant of certiorari was prior to decision by the Court of Special Appeals.
Our review of the decision of the Board of Trustees, like the circuit court’s, is based on the test set forth in the Administrative Procedure Act, specifically § 255 (g) of Art. 41, which states:
“(g) Affirmance, remand, reversal or modification of decision. — The court may affirm the decision of the agency or remand the case for further proceedings; or it may reverse or modify the decision if the substantial rights of the petitioners may have been prejudiced because the administrative findings, inferences, conclusions, or decisions are:
[362]*362“(5) Unsupported by competent, material, and substantial evidence in view of the entire record as submitted; or
“(8) Arbitrary or capricious.”
As Judge Eldridge so recently said for the Court in Bulluck v. Pelham Wood Apts., 283 Md. 505, 390 A. 2d 1119 (1978), “[substantial evidence,” as the test for reviewing factual findings of administrative agencies, is such relevant evidence as a reasonable mind might accept as adequate to. support a conclusion. We summarized the applicable law in Bulluck, with an extensive citation of authorities, as follows:
“The scope of review ‘is limited “to whether a reasoning mind reasonably could have reached the factual conclusion the agency reached.” ’ [Citations omitted.]
“In applying the substantial evidence test, we have emphasized that a ‘court should [not] substitute its judgment for the expertise of those persons who constitute the administrative agency from which the appeal is taken.’ Bernstein v. Real Estate Comm., 221 Md. 221, 230, 156 A. 2d 657 (1959), appeal dismissed, 363 U. S. 419, 80 S. Ct. 1257, 4 L.Ed.2d 1515 (1960). We also must review the agency’s decision in the light most favorable to the agency, since ‘decisions of administrative agencies are prima facie correct,’ Hoyt v. Police Comm’r, 279 Md. 74, 88-89, 367 A. 2d 924 (1977), and ‘carry with them the presumption of validity,’ Dickinson-Tidewater, Inc. v. Supervisor, supra, 273 Md. at 256, Heaps v. Cobb, 185 Md. 372, 378, 45 A. 2d 73 (1945). Furthermore, not only is it the province of the agency to resolve conflicting evidence, but where inconsistent inferences from the same evidence can be drawn, it is for the agency to draw the inferences. [Citations omitted.]”
283 Md. at 512-13.
[363]*363Accord, Annapolis v. Annap. Waterfront Co,, 284 Md. 383, 396 A. 2d 1080 (1979).
As indicated, the statute predicates the award of disability benefits upon total and permanent incapacitation, whether mental or physical, resulting from an accident occurring in the performance of duty. Cases involving statutes authorizing the payment of accidental disability retirement benefits, as here, have been analogized to cases arising under the workmen’s compensation law which require that an injury, to be compensable, must be accidental. See Minch v. Board of Trustees, 273 Md. 167, 327 A. 2d 889 (1974); Baker v. Board of Trustees, 269 Md. 740, 309 A. 2d 768 (1973); Board of Trustees v. Grandinetti, 269 Md. 733, 309 A. 2d 764 (1973). Thus, an injury, to be accidental under the retirement statute, must result “ ‘from some unusual strain or exertion of the employee or some unusual condition in the employment.’ ” Board of Trustees v, Grandinetti, supra, 269 Md. at 739, quoting from Kelly-Springfield Tire Co. v. Daniels, 199 Md. 156, 161, 85 A. 2d 795 (1952). Furthermore, an accidental injury “ ‘does not include unexpected results not produced by accidental causes.’ ” Baker v. Board of Trustees, supra, 269 Md. at 745, quoting from Vaughan v. Mayor & City Council of Baltimore, 229 Md. 547, 550-51, 184 A. 2d 842 (1962). An unexpected result (the incapacitating injury) attributable to a preexisting condition is not, therefore, an accidental injury.
In applying a comparable statutory provision in Baker, we affirmed the denial of accidental disability benefits to a marine engineer who claimed that an incapacitating heart attack he suffered was the result of striking his head on an overhead pipe in the course of his employment on a fireboat. In that case, we concluded “there was substantial evidence ... that Baker had a predisposition toward this sort of attack and that his head injury was not the direct cause of the myocardial infarction.” Id. at 744. See Vaughan v. Mayor & City Council of Baltimore, 229 Md. 547, 184 A. 2d 842 (1962); Williams v. McCardell, 198 Md. 320, 84 A. 2d 52 (1951) (both upholding denial of accidental disability benefits to firemen with history of arteriosclerotic heart disease who suffered heart attacks while on duty); Severn v. Baltimore City, 230 [364]*364Md. 160, 186 A. 2d 199 (1962) (upholding denial of accidental death benefits where the deceased had preexisting coronary artery disease); and Stancliff v. H.B. Davis Co., 208 Md. 191, 117 A. 2d 577 (1955) (death of an employee was not accidental when his preexisting cardiac condition was worsened by exposure to fumes).
In the present case, the Board premised its denial of accidental disability benefits upon its finding that Courtney had not suffered an “accidental injury” since his “nervous breakdown and mental disability [were] attributable to a preexisting condition of paranoia-schizophrenia.” Courtney argues that the record does not contain such relevant evidence as a reasonable mind would accept as adequate to support the Board’s findings. He maintains that Dr. Kastner offered the sole credible medical explanation of his breakdown, namely that his prior condition of paranoid schizophrenia had been in remission since 1964, that his 1975 disability was a new and separate illness, and that the 1975 breakdown was causally connected to the stress and strain he experienced in the performance of his duties as area branch librarian. However, as the Board noted, there was countervailing medical testimony that paranoid schizophrenia is a “recurrent disease, a disease which is often in remission and exacerbation” and that Courtney was suffering “a recurrence of it in 1975.” Dr. Kastner lent support to Dr. Freeman’s testimony by noting that “there are people that have recurrent episodes” of paranoid schizophrenia and that “no doctor knows the cause of schizophrenia or paranoia.” This statement served to undermine the force of Dr. Kastner’s prior assertion that Courtney’s 1975 mental incapacity was “caused” by his employment.
In essence then, the Board was confronted with conflicting expert medical opinion. It was the function of the Board to weigh the testimony and to judge its reliability. Heaps v. Cobb, 185 Md. 372, 45 A. 2d 73 (1945). Under the circumstances here, it cannot be said that “the Board was arbitrary, capricious or unreasonable in refusing on conflicting medical opinion, to accept the views favorable to [365]*365[Courtney’s] contentions.” Severn v. Baltimore City, 230 Md. 160, 168, 186 A. 2d 199 (1962).
We conclude from all the testimony that there was substantial evidence from which the Board could have reasonably found, as it did, that Courtney had a preexisting psychotic tendency and that the conditions of his employment did not cause his mental disability.2
Judgment affirmed; costs to be paid by appellant.